U.S. cancer deaths declined for the second year in a row in 2004, but there are worrisome signs that progress could falter, according to a new report from the American Cancer Society.

Deaths fell by 3,014 following a decline of 369 deaths in 2003. While the number of cancer deaths in women increased slightly in 2003, the number fell for both sexes in 2004 – the first time since the government began keeping death statistics in the 1930s.

The death rate for all cancers combined has dropped for 12 consecutive years, a total of 13.6 percent from 1991 to 2004. But that drop was smaller than the population growth for the first 10 years, so that an actual decline in the number of deaths did not occur until 2003.

The drop “is a remarkable sign that we have the potential to turn back deaths from cancer,” said John R. Seffrin, chief executive of the cancer society. “But this report shows that we have been losing momentum in some key areas that have been critical to our success.”

Among other crucial factors, declines in adult and youth tobacco smoking have leveled off and mammography is still not reaching a third of the population at risk.

Nearly a third of all cancer deaths this year will be a direct result of smoking, the report said, and another third are attributable to poor nutrition, obesity and physical inactivity. Many deaths in the remaining third could be prevented by screening to detect cancers early, while they are still treatable.

But progress in controlling tobacco use by both adults and adolescents has stalled, probably because tobacco industry efforts to promote smoking outspent control programs 23 to 1.

Obesity is another important risk factor, and it has been rising dramatically, doubling in adults to 33.3 percent between 1976 and 2004 and tripling in adolescents to 17.1 percent. Only one-third of youths are physically active for at least 60 minutes for five days per week, but 40 percent watch television for at least three hours per day.

Screening programs are underutilized, Seffrin said. Among women over 40, 69.7 percent have had a mammogram in the past two years. For women without health insurance, the figure drops to 40.2 percent.

Screening for colorectal cancer – the second leading cause of cancer deaths behind lung cancer – has fared even worse. A little more than 42 percent of people over 50 have had either a fecal occult blood test in the last year or a colonoscopy in the last five years. If such screening were universally employed, the report said, half of the 52,180 deaths expected this year could be prevented.

“This report points to how much more we could do if we utilized the lifesaving tools at our disposal,” Seffrin said.